Most of processes found in the literature to form silicon-heteroatom and germanium heteroatom bonds involve the reaction of a chlorosilane and a nucleophile (amine, phosphine, etc.). These reactions are based on a net dehydrohalogenation thus forming one equivalent of a hydrogen halide which needs to be scavenged by a base, forming large amounts of salt which need to be filtered out. This fact also limits the scope of the reaction to base-compatible substrates and results in products contaminated with a halogens such as chlorine and aminohalogens.
Silane compounds such as monosilane, disilane and trisilane are used in a variety of applications. In the field of semiconductors, silane compounds are frequently used as starting materials (precursors) for the production by chemical vapor deposition (CVD) of silicon-based dielectric films of, e.g., silicon nitride, silicon oxide, or silicon oxynitride. More specifically, silane compounds can produce silicon nitride by reaction with a nitrogen-containing reaction gas such as ammonia, silicon oxide by reaction with an oxygen-containing gas such as oxygen, and silicon oxynitride by reaction with a nitrogen-containing gas and an oxygen-containing gas.
At present the standard method for producing silicon nitride films by CVD involves inducing a reaction between ammonia gas or other amine (the amino compound) and a halosilane such as chlorosilane (the silane compound); however, ammonium chloride or amine hydrochloride is produced as a by-product by this reaction. Ammonium chloride is a white solid and as such accumulates in and clogs the exhaust lines of the CVD reaction apparatus. Amine hydrochloride salts are highly undesirable contaminants in aminosilanes used for electrical applications because they can react with metals in the CVD chamber and degrade the electrical properties of the semiconductor material or lead the creation of other types of defects. More than that, these salts are known to sublimate by a dissociation-recombination process generating HCl. Hydrogen chloride is a corrosive gas that can damage any process taking place in the CVD chamber as well as the chamber itself. Reactive chlorine from these or any other sources may cause these deleterious effects. Silane compounds synthesized without using halogen containing reactants thereby being free of halogens and aminohalogens are highly desirable.
In CVD methods, it is therefore desired to have a precursor compound that is halogen free.